The present invention relates to a method for the separation of a mixture of a single type of plastic or many types of plastics and a contaminant or a number of contaminants. More particularly, it relates to a method for the separation of a mixture of particles or flakes of a plastic or plastics which have a density between 1 and 1.4 grams/cc and a contaminant or contaminants which have a density greater than 1.6 grams/cc. The present method is used primarily for the recycling of plastic bottles and containers.
The usual practice in the recycling of bottles composed of plastic is to grind the bottles into particles or flakes so that the plastic can be recovered for use in new plastic articles. Normally, a plastic bottle is ground together with other plastic bottles which results in the recovery of only plastic flakes. There are times, however, when plastic bottles are ground together with aluminum and/or glass containers which results in a mixture of plastic flakes and undesirable contaminants. The aluminum and/or glass contaminants must be extracted from the plastic flakes before the plastic can be used for the manufacture of new plastic articles.
Various methods have been developed heretofore in order to separate a mixture of a plastic and a contaminant. For example, two prior art methods are disclosed in U.S. Pat. Nos. 3,516,841 and 4,368,274. U.S. Pat. No. 3,516,841 discloses a method whereby a mixture of a plastic and a contaminant are separated by flotation in a one-phase density solution. U.S. Pat. No. 4,368,274 discloses a method of separating a mixture of polyethylene terephthalate (PET) and aluminum flakes by applying a chemical which dissolves aluminum in a mixture. The PET may then be recovered.